Patent Literature 1 describes a driver circuit (i.e., power supply device) that supplies power to LEDs (Light Emitting Diodes) adopted as vehicle headlights. As shown in FIG. 12, the circuit includes a DC-to-DC converter 40x that supplies power to LEDs 10 by stepping up a battery voltage and a shunt resistor Rs connected to a cathode side (i.e., low-potential side) of the LEDs 10. The DC-to-DC converter 40x detects a drive current (see an arrow Y1 in the drawing) flowing through the LEDs 10 on the basis of an amount of a voltage drop across the shunt resistor Rs and performs a feedback control on an amount of power to be supplied to the LEDs 10 for the detection value to coincide with a target value.
In the event of a ground fault on the cathode side of the LEDs 10 as indicated by an arrow Y2 in the drawing, the detection value due to the shunt resistor Rs no longer takes a value corresponding to the drive current, owing to which the DC-to-DC converter 40x fails to perform the feedback control properly. In other words, when a ground fault occurs, most of the drive current flowing through the LEDs 10 flows to the ground fault side and the detection value due to the shunt resistor Rs becomes lower than a value comparable to the drive current. The DC-to-DC converter 40x thus performs the feedback control so as to increase the detection value to the target value. Accordingly, the drive current is increased further and a concern is raised about damage of the LEDs 10 given by an excessive drive current that flows through the LEDs 10.
In the related art, a ground fault detection circuit 30x stops an operation of the DC-to-DC converter 40x by determining that a ground fault occurs on the cathode side of the LEDs 10 when the detection value fails to rise to or above a predetermined value after an elapse of a certain time since a supply of power to the LEDs 10 is started.